Disorders of attention, social, and communicative functioning have become a significant public health concern yet we lack a systematic data base characterizing the typical development of basic building blocks that support optimal developmental outcomes. Attention is the gateway to all we perceive, learn, and remember, however, it remains a significantly understudied topic in developmental science. Typically developing infants show heightened attention to faces, voices, and infant directed speech and this is critical for scaffolding cognitive, social, and language development. In contrast, children with autism show social orienting impairments marked by decreased attention to these stimuli as compared with nonsocial events, and serious deficits in social and communicative functioning. These capabilities depend critically on early attention and intersensory processing skills, the ability to integrate information across the senses, particularly in dynamic faces, voics and social events. However, there currently are no individual difference measures of intersensory processing for infants or young children and the pathways by which intersensory processing skills affect attention and later social, cognitive, and language development remain poorly understood, presenting serious obstacles to identifying the emergence of atypical developmental patterns in infancy. The present proposal addresses these needs. We have developed the first two individual difference measures of attention and intersensory processing that can be used with infants and young children. They assess attention orienting, disengaging, maintenance and speed and accuracy of intersensory processing for dynamic, audiovisual social and nonsocial events. The present proposal will provide the first longitudinal data sets revealing developmental trajectories for these basic building blocks of attention and intersensory processing in typical development across 3 to 42 mos of age (Aims 1 and 2). This will provide a critical basis for identifying atypical developmental trajectories. Using a structural equation approach to growth curve modeling, we will then test models of association between developmental trajectories for these measures with cognitive, social, and language outcomes at 18, 30, and 42 mos (Aim 3). This will elucidate the most viable models of influence through which intersensory processing and attention skills affect social, cognitive, and language outcomes, contributing to developmental theory, knowledge, and guiding interventions. Finally, we develop and test a procedure for training intersensory processing skills and assess its effectiveness in a transfer test (Aim 4). Improvement and the conditions that foster it will lay a foundation for developing intersensory interventions. These goals have high health relevance. They will reveal the typical development of infant attention and intersensory processing skills and their effects on child outcomes, providing the first systematic body of basic research designed to be relevant and easily translated to identifying early atypical trajectories of attentin and intersensory processing and guiding interventions.